1. Field of the Invention
The present invention relates to a novel structure of an image forming apparatus such as an electrostatic printer or a copying apparatus.
2. Description of the Related Art
In general, an electrostatic printer includes a photoconductive drum around which a series of elements are arranged for forming a latent image on the surface of the drum, developing a toner image from the latent image, and transferring the toner image to a medium. These elements include a precharger, a latent image former, a developer, a transfer charger, a discharger and a cleaner. A hopper is provided for accommodating a medium to be printed in a cut sheet form. A series of rollers are provided for conveying the medium through the printer, including a pickup roller for removing the cut sheets one by one from the hopper, a registration roller for introducing the cut sheets into the image-transferring zone, a guide roller for guiding the cut sheets in synchronism with the rotation of the photoconductive drum during the image transferring operation, a heat roller for fixing the toner image on the cut sheets, and an eject roller for discharging the cut sheets from the printer.
The conventional electrostatic printer having such a structure has the driving system shown diagrammatically shown in FIG. 24. Namely, each of the rotating elements, i.e., the photoconductive drum and roller, is provided with a magnetic clutch for selectively connecting each element with a drive source (an electric motor). Thus, the respective rotating elements can be independently controlled. Magnetic clutches, however, are expensive, and the provision of same increases the cost of manufacturing the printer. Morever, the size of the printer is necessarily increased.
Further, in the conventional printer, if a jam occurs during the printing operation, clearing the jam by manually rotating a roller is difficult because the roller is always connected to a motor through a gear train.